<!-- gallery -->
    <div class="gallery">
        <div class="galleryUp">
            <h2>GALLERY</h2>
            <div class="line"></div>
            <p>Lorem Ipsum is simply dummy text of the printing and typesetting</p>
            <p>industry. Lorem Ipsum has been the industry's standard dummy</p>
            <p>text ever since the 1500s.</p>
        </div>

        <div class="galleryDown">
            <dl>
                <dt><img src="./images/03-01.jpg" alt=""></dt>
                <dd>Science Lab</dd>
            </dl>

            <dl>
                <dt><img src="./images/03-02.jpg" alt=""></dt>
                <dd>Indoor Stadium</dd>

            </dl>

            <dl>
                <dt><img src="./images/03-03.jpg" alt=""></dt>
                <dd>Transportation</dd>
            </dl>

            <dl>
                <dt><img src="./images/03-04.jpg" alt=""></dt>
                <dd>Kids Room</dd>
            </dl>

            <dl>
                <dt><img src="./images/03-05.jpg" alt=""></dt>
                <dd>Meditation Classes</dd>

            </dl>

            <dl>
                <dt><img src="./images/03-06.jpg" alt=""></dt>
                <dd>Kids Play Ground</dd>
            </dl>

        </div>
    </div>

    <!-- footer -->
    <footer>
        <p>&copy;&nbsp;2016&nbsp;imooc.com&nbsp;京ICP备13046642号</p>
    </footer>
</body>

.gallery .galleryUp h2{
    font-size: 32px;
    text-align: center;
    padding-top: 30px;
}

.gallery .galleryUp .line{
    width: 60px;
    height: 3px;
    background: #07cbc9;
    margin: 10px auto;
}

.gallery .galleryUp p{
    text-align: center;
    color: gray;
    font-size: 14px;
}

.gallery .galleryDown{
    width: 1200px;
    height: 650px;
    margin: 0 auto;
    /* background-color: #07cbc9; */
}

.gallery .galleryDown dl{
    overflow: hidden;
    float: left;
    width: 360px;
    height: 290px;
    margin: 15px 20px;
}

.gallery .galleryDown dl dt img{
    display: block;
}


.gallery .galleryDown dl dd{
    color: white;
    background-color: black;
    height: 50px;
    font-size: 16px;
    padding-left: 10px;
    padding-top: 10px;
}


footer{
    height: 80px;
    background-color: #07cbc9;
    text-align: center;
    line-height: 80px;
    font-size: 15px;
}

问题描述：

老师，我为了让文字不贴边给dd标签加了padding，但是为什么dd标签黑色的背景没有对上呢？​